In high performance internal combustion engines, it is frequently desirable to have the capability of changing the valve lifter rocker arm leverage ratio to adapt engine performance to suit certain atmospheric conditions and physical characteristics of the racetracks. It is common practice to accomplish this change by the physical substitution of an entire rocker arm having the desired leverage ratio, a procedure which is costly from the standpoint of both time and money.
There have been attempts in the past to vary the ratio of the lengths of rocker arms in valve lifter mechanisms to increase the lift obtainable. One structure for doing this is shown in U.S. Pat. No. 1,654,020 to B. F. Schmidt. The Schmidt device utilizes complementary mating surfaces on the rocker arm and pushrod end to produce a rolling contact which changes the effective rocker arm ratio in a predetermined variable fashion in accordance with the vertical motion of the pushrod. A screw thread adjustment of the pushrod length is provided.